This invention relates to novel piperidine derivatives of formula (I) and a process for the preparation thereof. wherein                R1 is H or C1-C6alkyl wherein the C1C6alkyl moiety is straight or branched;        R2 is —COOH or —COOalkyl wherein the alkyl moiety has from 1 to 6 carbon atoms and is straight or branched; orstereoisomers or pharmaceutically acceptable acid addition salt thereof.        
Terfenadine, α-[4-(1,1-dimethylethyl)phenyl]-4-(hydroxydiphenylmethyl)-1-piperidinebutanol, is a known antihistaminic agent which is currently available commercially under the name Seldane® with a recommended dosage of 60 mg b.i.d. (See PHYSICIAN'S DESK REFERENCE, 52nd Edition, 1998, pp. 1238-1244, Medical Economics Data, a division of Medical Economics Company, Inc. Montvale, N.J.). Terfenadine is disclosed in U.S. Pat. No. 3,878,217, issued Apr. 15, 1975. Sorken and Heel have provided a review of the pharmacodynamic properties and therapeutic efficacy of terfenadine [Drugs 29, 34-56 (1985)].
Terfenadine undergoes extensive (99%) first pass metabolism to two primary metabolites (fexofenadine) and an inactive dealkylated metabolite. Fexofenadine, a.k.a. 4-[1-hydroxy-4-[4-(hydroxydiphenyilmethyl)-1-piperidinyl]butyl-α,α-dimethyl-benzeneacetic acid, has been disclosed as an antihistaminic agent having oral activity in U.S. Pat. No. 4,254,129, issued Mar. 3,1981. It is currently available commercially under the name Allegra® (See PHYSICIAN'S DESK REFERENCE, 52nd Edition, 1998, pp. 1189-1190, Medical Economics Data, a division of Medical Economics Company, Inc. Montvale, N.J.).